标题: | 探讨与改进氮化物材料光电及微电子元件之特性 Investigation and Improvement of Performance in GaN-based Optoelectronic and Microelectronic Devices |
作者: | 林炳成 Lin, Bing-Cheng 郭浩中 李柏璁 Kuo, Hao-Chung Lee, Po-Tsung 光电工程研究所 |
关键字: | 氮化物;发光二极体;雷射;电晶体;Nitride;Light-emitting diodes;VCSELs;HEMTs |
公开日期: | 2015 |
摘要: | 近年来,宽能带与直接能隙IIIV族氮化物材料愈来愈受到重视,它具有可调变发光波长从紫外到蓝绿光的特性,及独特的高崩溃电压、高电子饱和速度等材料性质,使得IIIV氮化物已被广泛的应用在发光二极体、垂直共振腔面射型雷射及高电子迁移场效电晶体等元件上。在发光二极体方面,最期待的固态照明应用仍在发展中,尽管利用图形化蓝宝石基板增加光萃取效率及磊晶品质,已达商业化之标准,但发光二极体在高电流操作下的效率下降问题仍有待解决。在雷射应用方面,与传统的边射型雷射比较,垂直共振腔面射型雷射具有低发射角的圆型雷射光点及低制作成本等优点,如何进一步优化垂直共振腔面射型雷射的结构,降低雷射的临电流及提高斜率效率,乃是许多学者及研究团队之目标。随着电力电子的蓬勃发展,未来的高频段、高功率应用上氮化物材料之高电子迁移场效电晶体会是极佳的选择,如何降低元件之漏电流及提高崩溃电压是努力之方向。 在本研究中,我们利用铝含量渐变增加的电子阻档层来改善蓝光发光二极体的效率下降现象。从APSYS模拟之能带图、电场图、载子分布及电流密度等图形,显示了铝含量渐变增加之结构可以有效地增加电洞注入效率及局限电子之能力。并且实验结果也显示了效率下降现象大幅改善。 在第二部分中,我们在磊晶结构中应用了成份渐变的超晶格结构取代了传统的电子阻档层来降低效率下降。首先利用渐变成份的超晶格电子阻档层消除在最后氮化镓量子能障与电子阻档层间的极化效应,进而同时增加电洞注入及电子局限能力。在适当的渐变成份下,不但可以减少效率下降现象,更能够大幅提升高电流操作时的光输出功率。 接着,为了提高紫外光发光二极体之发光效率及磊晶层之晶格品质,我们利用反应式电浆沉积氮化铝缓冲层在紫外光发光二极体上。从材料分析结果,显示氮化铝缓冲层可以有效抑制缺陷,进而增加内部量子效率。从模拟结果显示若将此紫外光发光二极体制作成覆晶结构,此氮化铝缓冲层更可增加光萃取。因此可以增加紫外光发光二极体的光输出功率及减缓效率下降现象。 在第四部分中,我们在垂直共振腔面射型雷射中应用了能带工程化概念来降低临界电流及提高斜率效率。首先,利用渐变成份电子阻档层减少因极化产生的能带弯曲效应,进而同时增加电洞注入及减少电子溢流。经过适当的成份渐变电子阻档层设计,可以降低雷射之临界电流,更可增加雷射之斜率效率。 在第五部分中,我们使用碳掺杂的氮化铝/氮化镓超晶格结构成长在高电子迁移场效电晶体结构。从材料分析结果,显示氮化铝/氮化镓超晶格结构可以提高磊晶品质,并且降低垂直方向之漏电流,因此能有效地增加电晶体的崩溃电压与改善电晶体特性。 最后期许此篇论文可以帮助解决IIIV氮化物光电及微电子元件所遭遇之问题。 III-Nitride materials has been intensively studied over the past few decades. It has remarkable material properties not only for optoelectronic devices but also application in microelectronic devices. The III-Nitride materials have excellent properties such as wide direct bandgap, high breakage voltage, high electron mobility, and high operation frequency. These properties make III-Nitride materials very attractive for application in blue/ultraviolet light-emitting diodes (LEDs), blue vertical-cavity surface-emitting lasers (VCSELs), and high electron mobility transistors (HEMTs). Although these devices have been development by different techniques, enhanced performance is still essential. The motivation of this work is to figure out the method that can be used to improve the device performance sufficiently. First part, a tapered AlGaN electron blocking layer (EBL) with step-graded aluminum composition is analyzed in blue LED numerically and experimentally. The simulation results demonstrated that such tapered structure can effectively enhance the hole injection efficiency as well as the electron confinement. Consequently, the LED with a tapered EBL grown by metal-organic chemical vapor deposition (MOCVD) exhibits reduced efficiency droop behavior of 29% as compared with 44% for original LED, which reflects the improvement in hole injection and electron overflow in our design. In the second part, blue LEDs with graded-composition AlGaN/GaN superlattice (SL) EBL were designed and grown by metal-organic chemical vapor deposition. The simulation results demonstrated that the LED with a graded-composition AlGaN/GaN SL EBL have superior hole injection efficiency and lower electron leakage over the LED with a conventional AlGaN EBL or with a normal AlGaN/GaN SL EBL. Consequently, the efficiency droop can be alleviated to be about 20% from maximum at injection current of 15 to 120 mA, which is smaller than that for conventional AlGaN EBL (30%). The corresponding experimental results also confirm that the use of a graded-composition AlGaN/GaN SL EBL can markedly enhance the light output power by 60%. In the third part, flip-chip ultraviolet light-emitting diodes (FCUV-LEDs) on patterned sapphire substrate (PSS) at 375 nm were grown by an atmospheric pressure MOCVD. A specialized reactive plasma deposited (RPD) AlN nucleation layer was utilized on the PSS to enhance the quality of the epitaxial layer. By using high-resolution X-ray diffraction, the full-width at half-maximum of the rocking curve shows that the FCUV-LEDs with RPD AlN nucleation layer had better crystalline quality when compared to conventional GaN nucleation samples. As a result, a much higher light output power was achieved. The improvement of light output power at an injection current of 20 mA was enhanced by 30%. Further photoluminescence measurement and numerical simulation confirm such increase of output power can be attributed to the improvement of material quality and light extraction In the fourth part, the design and fabrication of GaN-based VCSELs with a composition-graded electron blocking layer (GEBL) are revealed experimentally and theoretically. It has been demonstrated that the laser output performance is improved by using a GEBL when compared the typical VCSEL structure with rectangular EBL. The output power obtained at 20 kA/cm2 is enhanced by a factor of 3.8 by the successful reduction of threshold current density from 12.6 kA/cm2 to 9.2 kA/cm2 and the enlarged slope efficiency. Numerical simulation results also suggest that the improved laser output performances are due mainly to the reduction of electron leakage current and the enhanced hole injection efficiency in the multiple-quantum-well (MQW) active region. In the fifth, the carbon-doped AlN/GaN superlattice (AlN/GaN SL) structure was introduced into the epitaxial growth of AlGaN/GaN HEMTs on Si (111) substrates, which could suppress the leakage from channel to substrate. Compared with conventional AlN/AlGaN double under layer (DUL) structure for AlGaN/GaN HEMTs, the results of electric properties imply that the vertical leakage can be dramatically decreased as two and half times as the carbon-doped AlN/GaN SL structure was introduced. Therefore, a threshold voltage of 2.0 V and maximum drain current of 175 mA/mm at the VGS of 2 V could be achieved. The output of this dissertation provide a great help on enhancing performance in GaN-based optoelectronic and microelectronic devices. |
URI: | http://140.113.39.130/cdrfb3/record/nctu/#GT070080517 http://hdl.handle.net/11536/125557 |
显示于类别: | Thesis |